Star schema

Star schema

Star schema is the simplest form of data warehouse schema. A star schema consists of at least one fact table and a number of dimension tables. These tables are relational database tables, often stored in SQL Server. The star schema source tables are not required to be stored in SQL Server. In fact, many OLAP solutions use other relational database management system (RDBMS) platforms, to hold source star data. It is called a star schema because the entity-relationship diagram between dimensions and fact tables resembles a star where one fact table is connected to multiple dimensions.

A star schema fact table consists of at least two types of columns: keys and measures. Keys are foreign key (FK) values that relate rows in the fact table to rows in the dimension tables. Measures are numeric values—usually, but not always, additive—that express the business metrics.